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Practical application of tannic acid is limited because it readily binds proteins to form insoluble aggregates. In this study, tannic acid was self-assembled with fish scale gelatin hydrolysates (FSGH) to form stable colloidal complex nanoparticles. The nanoparticles prepared from 4 mg ml(-1) tannic acid and 4 mg ml(-1) FSGH had a mean particle size of 260.8 ± 3.6 nm, and showed a positive zeta potential (20.4 ± 0.4 mV). The nanoparticles acted as effective nano-biochelators and free radical scavengers because they provided a large number of adsorption sites for interaction with heavy metal ions and scavenging free radicals. The maximum adsorption capacity for Cu(2+) ions was 123.5 mg g(-1) and EC50 of DPPH radical scavenging activity was 21.6 ± 1.2 μg ml(-1). Hydroxyl radical scavenging effects of the nanoparticles were investigated by electron spin resonance spectroscopy. The copper-chelating capacity and free radical scavenging activity of the nanoparticles were associated with their capacity to inhibit Cu(2+) ion-induced barrier impairment and hyperpermeability of Caco-2 intestinal epithelial tight junction (TJ). However, α-amylase inhibitory activity of the nanoparticles was significantly lower than that of free tannic acid. The results suggest that the nanoparticles can ameliorate Cu(2+) ion induced intestinal epithelial TJ dysfunction without severely inhibiting the activity of the digestive enzymes.

N-acetyl-β-D glucosamine (GlcNAc) is wildly used in cosmetics, nutraceuticals and pharmaceuticals. The traditional chemical process for GlcNAc production from chitin causes serious acidic pollution. Therefore, the enzymatic hydrolysis becomes a great promising and alternative strategy to produce GlcNAc. β-N-acetylglucosaminidase (NAGase) can hydrolyze chitin to produce GlcNAc. Here, a GH3 family NAGase encoding gene BlNagZ from Bacillus licheniformis was expressed extracellularly in Escherichia coli guided by signal peptide PelB. The recombinant BlNagZ presented the best activity at 60°C and pH 5.5 with a high specific activity of 13.05 U/mg. The BlNagZ activity in the fermentation supernatant can reach 13.62 U/mL after optimizing the culture conditions, which is 4.25 times higher than optimization before. Finally, combining BlNagZ with chitinase ChiA we identified before, chitin conversion efficiency to GlcNAc can reach 89.2% within 3.5 h. In all, this study provided not only a high active NAGase, and a secreted expression strategy to reduce the cost of production, which is conducive to the industrial application.